Camera used: K3 (as usual - nothing changed)
I usually have fairly decent JPEG files size after importing the RAW(DNG) file into CS5.
Today, I've checked a few files and I found that some RAW files at 29MB resulted into 10MB JPEG files.
Maybe I am now doing something wrong, or something has changed in my CS5 settings, but I think that the resulting JPEG files should be larger??

If they are "simple" in some sense (not a lot of variation in intensity across the image and/or low contrast (not many abrupt changes in brightness)) compression sometimes results in significant reduction in file size. Astronomical star fields, for example, may do this.

Shot at ISO 100; f5.6;
The original RAW(DNG) file is 28.6 MB.
The resulting image/file size is 6016 x 4000 pixels @ 9.07MB.
Type of image: distant blue bird on a treetop (spruce tree) with fairly bright/bluish sky.
I think that it is converted via CS5 at the highest possible JPEG quality ... ? Where is that in CS5 anyway (maybe something was changed and I did not notice it) ?

Yes, I realize that compression will give a smaller file size but I think I was expecting more MB (JPEG) from such a large (RAW) original file.

Same resolution as the raw file and at max JPEG quality out of photoshop, a jpeg about a third the size of the raw file (in MB) is pretty normal. Depends on the content as mentioned, but this is certainly not unreasonable.

One location for the quality settings in PS are in the save dialog when you 'save as' and switch the file type to jpeg (in CS4 at least).

My full size jpegs from the K-3II range in size from 6,500kb to 13,500kb. Actual size will mostly depend on the detail in the photograph. Something with a lot of sky or areas of fairly little change will result in smaller file sizes.

If it a plain blue sky and represents a relatively a large part of the image, then yes, the jpeg will be smaller than what you might expect from, say, a detailed landscape. All that homogeneous blue is capable of being heavily compressed as there is little detail within it to preserve.

Do you print a lot of pictures ? Is there a need to have such large jpg files? What is your monitor resolution?

I don't print a lot, no.
Monitor: 1920 x 1080
Why do you ask about keeping large JPEG files ???

---------- Post added 07-16-17 at 10:10 PM ----------

Originally posted by BrianR

Same resolution as the raw file and at max JPEG quality out of photoshop, a jpeg about a third the size of the raw file (in MB) is pretty normal. Depends on the content as mentioned, but this is certainly not unreasonable.

One location for the quality settings in PS are in the save dialog when you 'save as' and switch the file type to jpeg (in CS4 at least).

Just checked CS5 ... can't see any options for JPEG quality in there
I recall having seen something like that somewhere ... God knows where!

---------- Post added 07-16-17 at 10:15 PM ----------

Thanks:BrianR, jatrax, southlander, astrodave, hcc , pschlute for providing more info.
Now I know what's going and I appreciate the information from all of you good folks!

Camera used: K3 (as usual - nothing changed)
I usually have fairly decent JPEG files size after importing the RAW(DNG) file into CS5.
Today, I've checked a few files and I found that some RAW files at 29MB resulted into 10MB JPEG files.
Maybe I am now doing something wrong, or something has changed in my CS5 settings, but I think that the resulting JPEG files should be larger??

Any idea anyone?

Thanks!

Also, files that are predominantly one colour will compress more than files with many colours, lots of contrast, detail, dynamic range, etc. So some may be 10 megs, others as small as 3. Perfectly normal.

RE: monitor. Jpegs are primarily for online viewing, because they are very lossy, so you really only need 96 or 120 DPI, so your files could actually be smaller. I have a 27" iMac, so I do mine to fit my screen resolution, which is 2550 x 1440 or so - I leave some leeway, so I do 3000 on the long side @ 120 dpi. Most of my jPegs for viewing are around 3 megs. The new 5K scenes have way higher resolution, so I might have to reprocess stuff one day, but I always keep my DNG files.

If you're printing, you want TIFFs at 300 DPI or slightly higher. Those will be huge - 100 megs or more.

And if you want to learn CS, go to youtube - about a trillion video tutorials now, including stuff for CS5.

Also, files that are predominantly one colour will compress more than files with many colours, lots of contrast, detail, dynamic range, etc. So some may be 10 megs, others as small as 3. Perfectly normal.

at least in CS 6, the jpeg controls are all in the 'Export' dialogue box. You export the files after processing and save them somewhere else as jpegs. There are other ways to do it, but that's what happens in CS6, and I imagine CS5 isn't too different in that regard.

In Photoshop CS5 you choose “Save As” and from the window that opens you can choose the folder, the name, the format, etc.
Choosing the format “JPEG (*.JPG,*JPEG.JPE)” and hitting “Save”, opens a second window where you can change “Image Options”, where more “Quality” means less compression and thus bigger jpeg images (de default is 8 the maximum is 12).

As an example I saved a K-S2 DNG file (16,3 Mbytes in size) with quality 8, 10 and 12, and the results were 1.7, 3.8 and 10 Mbytes in size respectively.

In Photoshop CS5 you choose “Save As” and from the window that opens you can choose the folder, the name, the format, etc.
Choosing the format “JPEG (*.JPG,*JPEG.JPE)” and hitting “Save”, opens a second window where you can change “Image Options”, where more “Quality” means less compression and thus bigger jpeg images (de default is 8 the maximum is 12).

As an example I saved a K-S2 DNG file (16,3 Mbytes in size) with quality 8, 10 and 12, and the results were 1.7, 3.8 and 10 Mbytes in size respectively.